text/html2014-08-25T22:09:55+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.524136 -2.084263SO9491 : Electricity substation, Castle Mill Road, Dudleyhttp://www.geograph.org.uk/photo/4138044
Surrounded by newly built houses of the New Priory estate, this old electricity substation looks a little out of place. I'm not sure if it still fulfils its function or has just been left in place as a historic building.text/html2014-08-25T21:51:29+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.525655 -2.096352SO9391 : Breach in the Nodular Limestone Member, Wren's Nesthttp://www.geograph.org.uk/photo/4138003
Given that the Nodular Limestone was of no interest to the quarrymen because of its high sandstone content, I'm surprised that such a wide breach has been cut into the slab.text/html2014-08-25T21:47:46+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.526464 -2.096059SO9392 : Fossils in the Nodular Limestone Member, Wren's Nesthttp://www.geograph.org.uk/photo/4137992
Besides lots of fragments, there is a trilobite (or perhaps two, top left), a couple of brachiopods (shells, one bottom left), an orthocone (bottom centre-right) and some corals (bottom right), all in a space of perhaps 40cm across. Larger, annotated version: http://www.nearby.org.uk/geograph/media/files/33e75ff09dd601bbe69f351039152189/14060858a-original.jpgtext/html2014-08-25T21:13:26+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.526104 -2.096205SO9392 : Looking for fossilised corals, Wren's Nesthttp://www.geograph.org.uk/photo/4137915
At the top of a steep-sided ridge quarried on both sides, a plethora of reef-forming corals and other fossils can be found in the limestone. Members of the West Wales Geological Society are trying to identify some of them.text/html2014-08-25T21:01:54+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.526104 -2.096205SO9392 : Fossilised corals, Wren's Nesthttp://www.geograph.org.uk/photo/4137890
A reef bed (bioherm) near the top of the outcrop of the Nodular Limestone Member north of the ripple beds. The fragment shown is about 20cm wide. In addition to many rounded shell fragments and some limestone cement, a large coral can be seen on the right. The stems of the corals would be pointing into the rock (but are unlikely to be preserved).text/html2014-08-25T20:55:17+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.525655 -2.096352SO9391 : Nodular Limestone cliff, Wren's Nesthttp://www.geograph.org.uk/photo/4137880
This view shows the ripple beds from the side. The pure limestone layers on either side of the Nodular Limestone Member have been quarried, leaving this impressive slab standing on its own. The track in the foreground gives access to the quarry in the Lower Quarried Limestone Member, i.e. to the east (left) of the slab.text/html2014-08-25T20:32:38+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.524935 -2.096645SO9391 : Ripple beds, Wren's Nest (close-up)http://www.geograph.org.uk/photo/4137844
This close-up of the ripple beds in the Nodular Limestone Member shows the ripple patterns created by wave action when these rocks were deposited (before being folded up at this angle). This indicates that the surface of the sediment was near the wave base of coastal waters, i.e. that part of the seafloor which is never or rarely exposed but is always within reach of the turbulence of waves. While many of the cracks will be due to recent weathering, some of them may originate as sun cracks from occasional exposures of the sediment at exceptionally low tides. text/html2014-08-25T20:24:39+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.524935 -2.096645SO9391 : Ripple beds, Wren's Nesthttp://www.geograph.org.uk/photo/4137817
What looks at first like a concrete wall is the top of the Nodular Limestone Member of the Much Wenlock Limestone Formation. The rock face has been exposed by quarrying of the overlaying (younger) Upper Quarried Limestone Member in the past. The dip is too steep for soil to form on the surface. However, the exposure isn't totally flat: a wavy pattern has emerged due to wave action when these rocks were deposited - this is known as a ripple bed. The Nodular Limestone Member consists of thicker limestone layers interbedded with thinner sandstone, which explains the spalling off of large sheets as can be seen on the right.text/html2014-08-25T20:17:11+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.524305 -2.097381SO9391 : Fossil trench, Wren's Nesthttp://www.geograph.org.uk/photo/4137795
The fossil trench is an old quarry in the Upper Quarried Limestone Member of the Much Wenlock Limestone Formation. The slope to the left is scree made up of debris from the quarrying operation. It overlays the Nodular Limestone Member, which wasn't quarried because of its higher sandstone content. There are many fossil fragments to be found in the scree at this location, and picking a few for keeping is encouraged as long as no hammers are used.text/html2014-08-25T18:18:41+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.523496 -2.097379SO9391 : If I had a hammer...http://www.geograph.org.uk/photo/4137575
...I'd still not be allowed to use it. Anyone is allowed to pick fossils from the loose rock (within reason), but rock faces are strictly out of bounds. The wardens of the National Nature Reserve also suggest that the location from which any fossils have been collected is stored alongside each specimen, and that any unwanted specimens are sent to Dudley Museum.text/html2014-08-25T18:03:15+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.523406 -2.097084SO9391 : Nodular Limestone with bentonite layerhttp://www.geograph.org.uk/photo/4137549
At a quarry on the west side of Wren's Nest, a good insight can be had into the internal structure of the Nodular Limestone Member. Here thicker limestone layers alternate with thin bands of sandstone. The limestone is a deposit from shelly organisms living in a shallow shelf sea, while the sandstone is terrigenous, i.e. has been transported here by rivers after flooding events on nearby land. Amongst this, there are two thin and very crumbly layers. These are made up of bentonite, a clay deposit originating from volcanic ash. The shelly creatures clearly had to contend with quite a lot of environmental pressure, but the fact that limestone layers follow after each sandy or volcanic bed shows that they have been able to cope. Geologist's head shown for scale.text/html2014-08-25T17:48:36+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.520982 -2.093836SO9391 : Calcite vein in limestonehttp://www.geograph.org.uk/photo/4137521
Calcite is recrystallised calcium carbonate. While the limestone matrix is made up of ground fossil shells with some sand mixed in, the calcite in the vein is crystallised from solution. The specimen was found near the south end of Wren's Nest, where a fault line surfaces. The crack would have formed due to compressive stress near the fault. Subsequently, water has infiltrated the rock, dissolved some of the limestone and collected in the crack. Gradually, the solution has become supersaturated with calcium carbonate, and crystallisation has started from the surfaces adjoining the crack, gradually filling it up.text/html2014-08-25T17:39:40+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.520713 -2.093246SO9391 : Calcined limestonehttp://www.geograph.org.uk/photo/4137509
There are numerous lime kilns around the southern tip of Wren's Nest, where the local limestone would have been calcined in order to drive off carbon dioxide and turn the calcium carbonate mineral into calcium oxide. If there is any iron present in the rock, it will be oxidised to Fe(III), which causes a red colouration. Although I am not certain, this loose material could be the result of that process.text/html2014-08-25T17:29:34+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.521161 -2.094426SO9391 : Southern tip of Wren's Nesthttp://www.geograph.org.uk/photo/4137496
At this point, the quarried trenches of the Upper Quarried Limestone of the western side of the hill (left) and of the Lower Quarried Limestone of th eastern side (right) join together at right angles. This has come about because a fault running along the top of the ridge has pushed the western side up.text/html2014-08-25T17:15:20+00:00http://www.geograph.org.uk/profile/2520Rudi Winter52.527276 -2.092670SO9392 : Limestone quarry, Wren's Nesthttp://www.geograph.org.uk/photo/4137471
This ravine is a trench created by quarrying limestone from the Lower Quarried Limestone Member at Wren's Nest. To the left lies the (younger) Nodular Limestone Member, which wasn't quarried as it contains too much sandstone and would therefore have needed additional processing before it could be used in the iron smelting industry. These Silurian limestones were deposited while the area was in a shallow, tropical shelf sea. On the right lies the (older) Coalbrookdale Formation, a mudstone sediment deposited while this area was in deeper water in which shelly creatures couldn't live.